Modern electronic key telephone systems are typically marketed having a variety of systems sizes, station types, and feature combinations. Thus, the user can cost-effectively select the particular telephone system which best matches his needs in terms of system size (number of central office lines and number of station sets), type of station set utilized, and call feature capabilities. In some processor controlled key telephone systems, the operations of the system are controlled using preprogrammed read-only memories (ROMs) located on memory cards in a common control module.
A problem exists when a user decides to change system size, type of station set utilized, or features of his existing key telephone system. Typically, these system changes require the replacement of both hardware and memory circuit cards in the common control module. Undesirably, the replacement of the hardware and memory circuit cards often require the services of a skilled craftsperson to disassemble the common control module and make the desired changes to the system. What is desired is a simple, economic, and reliable arrangement to enable the user to make changes to the system without disassembling any part of the system.